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In the design of a wound rotor three-phase induction motor. Rotor Current per Phase Ir =
15 * [(Is*Ts)/Tr]
85 * [(Is*Tr)/Ts]
15 * [(Is*Tr)/Ts]
85 * [(Is*Ts)/Tr]
85 * [(Is*Ts)/Tr]
In the design of a wound rotor induction motor, the rotor current per phase (IrтАЛ) is related to the stator current (IsтАЛ) by the turns ratio between stator (TsтАЛ) and rotor (TrтАЛ) windings, adjusted by a transformation constant. The factor 0.85 represents the effective current transformation accounting for magnetizing current and leakage reactance in practical machine design.
In the design of a wound rotor induction motor, the rotor current per phase (IrтАЛ) is related to the stator current (IsтАЛ) by the turns ratio between stator (TsтАЛ) and rotor (TrтАЛ) windings, adjusted by a transformation constant. The factor 0.85 represents the effective current transformation accounting for magnetizing current and leakage reactance in practical machine design.
IrтАЛтЙИ0.85тЛЕIsтАЛтЛЕTrтАЛTsтАЛтАЛ тАФ Relation between rotor and stator currents
ATsтАЛтЙИATrтАЛ тАФ Ampere-turn balance principle
The rotor current is derived from the stator current via electromagnetic induction. Using the ampere-turn balance principle, the primary stator ampere-turns (IsтАЛ├ЧTsтАЛ) must be balanced by the secondary rotor ampere-turns (IrтАЛ├ЧTrтАЛ), considering the coupling coefficient and transformation losses approximated by the coefficient 0.85.
The constant 0.85 is an empirical design factor for wound rotor induction motors.
The ratio TsтАЛ/TrтАЛ represents the turns ratio per phase between the stator and the rotor windings.
The formula accounts for the necessity of higher rotor current due to slip-related frequency effects.
Allows for external resistance control to adjust starting torque.
High starting torque with low starting current.
More complex construction than squirrel-cage rotors.
Higher maintenance due to slip rings and brushes.
Conveyor systems requiring high starting torque.
Lifts and hoists.
The transformation factor 0.85 is specific to standard industrial design procedures for calculating rated rotor current.
Options A and C are incorrect as they invert the relationship or use incorrect constants.
D is correct тАФ The rotor current per phase IrтАЛ is calculated as 0.85├ЧTrтАЛIsтАЛ├ЧTsтАЛтАЛ.
Always verify the turns ratio orientation; for induction motors, TsтАЛ/TrтАЛ is used to reflect the stepping down of current from stator to rotor.